/Engine/Source/Runtime/SlateCore/Public/Application/SlateApplicationBase.h
Gets the active regular top-level window. A regular window is a non-menu, non-tooltip, non-cursor decorator window
The top level window, or nullptr if no Slate windows are currently active.
[TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [SWindow](API\Runtime\SlateCore\Widgets\SWindow) > GetActiveTopLevelRegularWindow() const